Berkshire reduced its ConocoPhillips holdings to 13.5 million shares at the end of September, down from 24.2 million shares in June. In an record-setting day for the Dow Jones industrial average, shares of XOM stock closed up 63 cents, 0.7%, to $93.22 Thursday. In after-hours trading, the stock added 85 cents, 0.9%, to $94.07.

But the size of the Exxon investment — worth $3.7 billion at Thursday’s closing price — suggests it was Buffett’s decision. Buffett has said investments smaller than $300 million are likely to be the work of other Berkshire managers.

Berkshire has previously invested in Exxon Mobil, but sold those shares in 2009.

At the same time, it appears Buffet and co. see good future in oil shares. In addition to XOM stock, Berkshire has investments in Phillips 66 and oil and gas industry supplier National Oilwell Varco.